1. Field of the Invention
This invention relates to a heat-sensitive recording material. More particularly, the present invention relates to a heat-sensitive recording material with excellent sensitivity and recorded image stability.
2. Description of the Prior Art
Heat-sensitive recorded materials generally comprise a substrate and a heat-sensitive recording layer provided on the substrate and containing, as main components, an ordinarily colorless or light-colored, electron-donating dye precursor and an electron-accepting color developer. When these materials are heated by a thermal head, a thermal pen, a laser beam or the like, the dye precursor and the color developer react with each other momentarily to form an image. They are disclosed in, for example, Japanese Patent Publication Nos. 4160/1968 and 14039/1970. Such heat-sensitive recording materials have various advantages such as records can be obtained by the use of relatively simple equipment, the maintenance of the equipment is easy and the equipment generates no noise; therefore, the recording materials are in wide use in such fields as recorders for measurement, facsimiles, printers, terminal equipments for computers, labels, automatic ticket machines and the like.
Heat-sensitive recording materials are required to have, as basic properties, sufficient image development sensitivity, sufficient developed image density, no deterioration of developed image with the lapse of time, etc. As the heat-sensitive recording materials have come in recent years to be used widely, they are required to further have image retainability such as image stability against oily matters (e.g. hairdressings, hand creams and oils and fats contained in sweat) adhered to the image, namely, grease resistance.
Adding a phenol type anti-oxidant to heat-sensitive recording materials as a stabilizer for improvement of retainability of the recorded image formed by these heat-sensitive recording materials is described in Japanese Patent Application Kokai (Laid-open) Nos. 45747/1974, 18752/1979 and 83495/1982. However, none of these approaches provides an additive which gives satisfactory image stability without reducing sensitivity.